Process for purifying zinc ore



Aug. s, 1933. o, GERLACH 1,921,743

PROCESS FOR PURIFYING vZINC ORE Filed July 2l, 1930 2 Sheets-Sheet 2Patented Aug. 8, 1933 UNITED STATES PATENT OFFICE PROCESS FOR PURIFYINGZINC ORE Oscar Gerlach, Peru, Ill., assignor to Matthiessen & HegelerZinc Co., La Salle, Ill., a Corporation of Illinois This inventionvrelates to' improvements in processes and apparatus for purifying zincore and the present invention is an improvement upon that described andclaimed in my prior co-pending application Serial No. 243,840, filedDecember 31, 1927, which has matured into United States Patent No.1,773,991, datedAugust 26, 1930. In said prior application there isdisclosed an improved process of purifying zinc ore according to whichthe ore is freed of lead,

cadmium and sulphur compounds and other impurities by the application ofheat in such a way that a portion of the body of the ore is heated at atemperature and pressure at which lead and cadmium vaporize while theremaining portion of the body of ore is maintained at a substantiallylower temperature so that the lead and cadmium which are volatilizedfrom the rst named portion are condensed in the second named portion andthereby rendered capable of separation. In the practice of that process,the entire body of ore subjected to the action of heat is ordinarily ofsubstantially uniform quality and after the heating process iscompleted, the upper layer, which has been freed of the lead and cadmiumcompounds. and from which the sulphur has been driven off, is separatedby a scraping device which removes the purified ore and leaves theremaining ore. containing the impurities, for subsequent treatment,

While that process of said prior application has been found to be verysatisfactory in commeicial use, it has been discovered that thepurification of the zinc ore may be carried on more efciently and morequickly by the improvement of the present invention according to whichdifferent grades of ore are superimposed upon each other in thepurifying apparatus and simultaneously subjected to the action of heatin such a manner that the better grade or grades of ore are puried morequickly than the residue and may be separated from the remaining layeror layers of ore for use in manufacturing zinc of the highest quality.

Many zinc companies, particularly those operating zinc rolling mills,use different grades of spelter, depending upon the purpose for whichthe rolled zinc is intended, and four different grades of spelter arecommonly specified. namely,

"high grade", intermediate, brass special and prime western. The lasttwo mentioned grades of spelter may be readily produced in a zincsmelter but the first two mentioned grades must be produced by theelectrolytic process, the redistillation process, or by the retortprocess, us-

ing the purified zinc ore produced by the process of my said priorapplication. The zinc smelters are ordinarily supplied with differentgrades of ore which are known as high grade, prime western andfloatation ores", which differ in the amount of impurities containedtherein. It is generally understood that a high grade ore is one whichcontains less than one-tenth of one per cent of lead and that a lowgrade or prime western ore is an ore which contains more than one-tenthof one per cent of lead, Without regard to the percentages of otherimpurities which may be contained in the ore. By the process of thepresent invention, these different grades of ore may be treatedsimultaneously in sintering apparatus, similar to that employed in thesintering of iron ores, whereby a zinc ore of a high grade of purity ismore quickly and efficiently obtained than is possible by the inventionof said application. Y

According to the present invention, the zinc ore to be treated isdivided into portions of high grade and low grade quality and the pansof the sintering machine are partially filled in succession with thelow'grade ore and then a layer 80 of the high grade ore is progressivelyfilled into the pans above the low grade ore. Both grades of ore havepreliminarily been crushed to a considerable degree of fmeness, forexample, that which would enable them to pass through a tenmesh screen,and they are preferably subjected to a preliminary roasting before beingplaced in the sintering machine in order that the major portion of thesulphur, about ninety per cent, maybe driven off before the ore issubjected to the action of heat. The zinc ore introduced 'into thesintering machine will have been converted by the roasting operation,which is ordinarily carried on at a temperature of from 1600 degreesFahrenheit to 1800 degrees Fahrenheit, from zinc sulphide (ZnS) intozinc oxide (ZnO) and this zinc ore is fed into the sintering machinethrough hoppers so that the different grades of ore are automaticallysuperimposed upon each other as the pans of the sintering machine movealong their endless path of travel. Some sulphur, usually about threeper cent, will remain in the ore when it is introduced into thesintering machine anda quantity of coal, coke or anthracite is alsopreferably mixed thoroughly with the ore before it is introduced intothe hoppers so that process. The heating of the ore is effected, as inthe prior process, by moving the sintering pans beneath a sintering hoodequipped with gas burners or other burners capable of producing a hightemperature therein sufficient to ignite the coal or sulphur containedin the material to be4 sintered, preferably a temperature of between2600 degrees Fahrenheit and 2800 degrees Fahrenheit. A number of burnersare preferably provided in this hood, the rst ones being fed with air oroil and gas to produce an oxidizing ame while the later ones ofthe'series are fed byv steam or oil and gas to form a reducing fiame andto cause the production of free vhydrogen which is made use of infreeing the zinc ore of the cadmium oxide contained therein. Tofacilitate the purification of the ore, a small quan- `tity of commonsalt (NaCl) is mixed with the top layer of high grade ore. This salt isvaporized by the heat and the vapors passing through the ore convert thelead oxide (PbO) into lead chloride (PbClz) which is more readily drivenoff from the top layer of ore and condensed in the lower layer as thesintering pans continue their travel.

The heat produced by the burners and the burning of the coal mixed withthe ore, causes the upper top layer of high grade ore tobe'substantially freed of both lead and cadmium compounds. The lead isdriven out of the upper layer of ore and collects partly in the lowgrade ore beneath the same in the form of sulphate or chloride (while apart escapes as such through the fan and stack to the air). The cadmiumis likewise driven out of the upper layer of high grade ore and collectspartly in the lower layer of low grade ore in the form of sulphate andsulphide, while a part thereof escapes. The zinc oxide in the upperlayer of ore is not driven out during the limited time in-which the oreis exposed to the flame. It appears that the lead and cadmium compoundsin the upper layer of high grade ore are reduced and then volatilized sothat they recombine in the vaporized state with sulphur and oxygen toform the sulphates and sulphides which are condensed in the lower layerof low grade ore. In this way, the upper layer of high grade ore issubstantially freed of cadmium and lead compounds and due to the highguality of this layer at the commencement of the operation, thepurification of the upper layer may be effected very rapidly while thelower layer, from which the upper puried layer is separated, may besubjected to further treatment or use in the manufacture of zinc of lowquality. The upper purified layer of zinc is separated from the otherand subsequently distilled in a retort with carbon to obtain free zinc.

Although various forms of apparatus might be employed in carrying on theprocess described above, there is illustrated in the accompanyingdrawings an improved sintering apparatus, similar to that employed inthe sintering of iron ore, except that certain improvements have beenadded for the purpose of adapting it to the practice of the presentprocess. In the drawings,

Fig. 1 shows a side elevation of the improved sintering machine;

Fig. 2 shows a partial longitudinal section through the upper row ofsintering pans showing the method of depositing the different layers ofore in these pans and the means for breaking up these layers andseparating the upper layer from the lower layer;

Fig. 3 shows a detail vertical section, on an enlarged scale, taken onthe line 3 3 of Fig. 1, showing the construction and mounting of thesintering pans and the means for drawing oil` the gases from beneaththese pans, and

. Fig. 4 is a detail section on the line 4-4 of Fig. 2, showing thedevice by which the upper layer of ore is broken up after heating inpreparation for its separation from the lower layer.

As illustrated in the accompanying drawings, the sintering machine 10comprises a plurality of sintering pans 11 which are mounted to followan endless path of travel and which form a substantially continuousseries so that, along the upper stretch of their path of travel, eachpan is located closely adjacent to the next leading and following `pansof the series. Since the pans are provided with bottom walls and sidewalls, but are Without end walls, it will be understood that the sidewalls and bottom walls, joining onto each other, form a continuousmovable trough, successive portions ofl which are progressively filledas the pans move beneath the feeding hoppers. The sintering pans 11 aresupported by a frame 14 comprising a plurality of vertical frame membersl5 and a number of transverse longitudinal frame members 16. The frame14 serves as a support for certain track members which are provided tocoact with rollers 17 mounted to revolve on trunnions 18 projectinglaterally from opposite sides of the sintering pans 11, as shown in Fig.3, there being two rows at each side of each pan. In the upperhorizontal portion of the path of travel of the sintering pans 11, therollers coact with horizontal trackways 19 having depending anges 19awhich are secured to brackets 20 attached to the longitudinal side framemembers 21. At the discharge end of the machine, the track members 19are curved downwardly in semicircular fashion, as shown at 19h, and arearranged to cooperate with the upturned semicircular eX- tremities 22bof the lower track members 22 which are attached to the vertical framemembers 15, thus forming a semicircular slot at the discharge end of themachine through which the rollers 17 travel as the sintering pans movedownwardly and are reversed in position. The lower track members 22 areinclined downwardly towardy the forward end of the machine and arethence curved upwardly in a semicircle as shown at 22c, thus guiding thesintering pans in their upward movements at the forward end of themachine. Each roller 17 has an annular flange 17a which projects overthe edges of the adjacent track members 19 and 22 so that lateraldisplacement of the sintering pans is prevented. The movement of thesintering pans 1l on the trackways 19 and 22 is effected by a pair ofdriving wheels 24 mounted on a transverse shaft 25 and journaled inbearings 26 which are secured to the longitudinal frame members 27adjacent the forward end of the machine. The driving wheels 24 areprovided with teeth 24a arranged in pairs, the teeth of one pair ,beingspaced apart from those of the nextadjacent pair in such a manner thatthe teeth of each pair will move downwardly over one of the rollers 17on a sintering pan l1 when this sintering pan has moved by gravity alongthe lower inclined tracks 22 from the rear end of the machine to theforward end thereof. As the rollers of the sintering pans are engaged bythe teeth 24a of the wheels 24, While these pans are in their reversedpositions, they are then moved by the wheels 24 around the curvedportion 22c of the lower trackways and brought into their uprightpositions where the rollers 17 pass onto the upper horizontal trackways19. The pans on the trackways 19 are then moved rearwardly by theengagement therewith of the next following pans 11 which arecontinuously elevated by the driving wheels 24 and moved onto thetrackways 19 at the forward end of the machine. The driving wheels 24are actuated by a series of reducing gears 28 which are mounted on ashaft journaled in suitable bearings carried by the frame of the machineand in turn driven by a pinion 29 fixed on the shaft of an electricmotor 3D. The reducing gears serve to actuate the driving wheels 24 at arelatively low speed so that' the sintering pans 11 have a relativelyslow travel in a rearward direction on the upper horizontal trackways19.

When a sintering pan 11 reaches the rear end of its path of travel onthe horizontal portions of the trackways 19, it falls by gravity aroundthe semicircular track members 19b and 22b and a gap 3l is preferablyprovided between adjacent pans at the beginning of this downwardmovement so that the initial movement of each pan and the engagementtherewith at the bottom of the gap with the next lower pan produces ajar suiicient to discharge the materials contained therein.

The extent of the gap 31 and the maintenance of a continuous series ofpans 1l along the upper horizontal portions of the trackways 19 isinsured by a pair of controlling wheels 32 mounted some distanceforwardly from the rear end of the machine and provided with teeth 32awhich engage the rollers 17 of the pans 11 on both their upper and lowerpaths of travel. The wheels 32 are mounted on a shaft 33 journaled inbearing blocks 34 which are adjustable in slides 35 and controlledthrough levers 36 by suspended Weights 36a. The wheels 32 are thusrotated by the advancing pans 1l along the upper trackways 19 and asthey rotate, they automatically vdischarge successive pans in invertedposition which are engaged by the lower portions of the wheels so that apredetermined number of pans ll are retained in position around thecurved trackways 19b and 22b with a predetermined gap 3l through whichthe pans fall successively from their positions on the upper horizontaltrackways 19.

The sintering pans 11 are provided with upwardly extending side walls11a connected by transverse bars 11b and these side walls 11a haveledges, as shown in Fig. 3, upon which are mounted the ends of thegrates 11c onto which the crushed ore is loaded. As before stated, thesintering pans/ are open at their ends so that when they are located inclose spaced relation on the upper trackways 19, as shown in Fig. 1,they form a continuous trough for the reception of the crushed ore. Inthe region beneath the sintering pans which are mounted upon the uppertrackways 19, there is located a casing 37 which forms a vacuum chamber38. The upper edges of the walls of the casing 37 are connected to arectangular frame 39 which is seated on and secured to the inturnedflanges 21a of the side frame members 21 and which forms a funnel fordirecting materials downwardly into the chamber 38. The chamber 38 haspipes 40 leading from the side thereof and connected to a suction pumpor other suitable apparatus adapted for maintaining a partial vacuum inthe chamber 38 so that the sulphur dioxide and other gases which areliberated in the ore, and not condensed or deposited therein, are drawninwardly into the chamber 38 and thence outwardly through the pipes 40.In order to form a seal between the vacuum chamber and the sinteringpans while these pans are in the upper part of their path of travel, asealing plate 4l, of somewhat flexible construction, is mounted alongeach lateral edge of the frame 39, being held in position by clampingmembers 42 engaging the threaded studs 43 which are secured to theopposite sides of the frame 39. By adjusting the clamping members 42,the upper edges of the sealing plates 41 may be caused to engage in thedesired manner the grooves 44 which are formed in the side members ofthe sintering pans on the under sides thereof so that the grooves insuccessive pans align accurately with each other. A seal is thus formedso that the gases from the sintering pans may be drawn down into thevacuum pan 38 without actual loss.

The crushed and wetted ores which are to be sintered in the machine l0are fed to the sintering pans 11 through hoppers positioned adjacent thefront end of the machine. The low grade of crushed ore 45 is fed from ahopper 46 and the high gradev of ore v47 is fed from a hopper 48. Thehopper 46 has its mouth positioned some distance below the upper edgesof the side walls 11a of the sintering pans so that as these pans travelbeneath the hopper 46a layer 45a of low grade ore is deposited in thepans with its upper surface located some distance below the upper edgesof the pans. The pans which are thus partially filled then pass beneaththe hopper 48 which has its mouth so located that it discharges into thepans an upper layer 47@l of high grade ore having its upper surfacelocated substantially fiush with the upper edges of the side walls 11aof the pans. The pans which are thus filled then pass successivelybeneath the burner hood 49 which, as above described, is preferablyprovided with two series of burners so that the desired action isobtained upon the ore through the application of heat. As the ore isheated, the lead and cadmium compounds are driven out of the upper layer47a and condensed in the lower layer 45a and the sulphur is driven offand drawn downwardly by the vacuum chamber 38. The heating of the upperlayer of ore and the combustion of the fuel mixed therewith, bringsabout a hard or crusted condition thereof and, to facilitate theseparation of the upper purified layer from the lower layer, means areprovided for breaking up the upper layer of ore at a point adjacent tothe discharge end of the machine. This breaking action is effected by asca'rier 50 which comprises a drum 51 mounted on a shaft 52 which-isjournaled in brackets 53 extending upwardly from the side frame membersof the machine.` The drum 51 lcarries a number of scarifying blades 54each of which extends radially outward from the drum 51 with a laterallyturned extremity 54a adapted to move in `a cylindrical path concentricwith the axis of the drum. The radial portions of these blades aremounted in slots 55 formed in the drum and are secured in adjustedposition by inclined set screws 56. By this arrangement, the blades areadjustable to cause the portions 54a to move in cylindrical paths ofdifferent diameter so that they may be caused to break up upper layers47a of different thickness. The shaft 52 of the'drum 5l is actuated bysuitable driving mechanism from the motor 30 and is preferably. drivenin the direction indicated by the arrow 57. After the crusted ore 47ahas been broken up by the scarier 50, it is removed from the lower layer45a by a bucket elevator 58 comprising endless chains 59 mounted totravel around gears 60 and having buckets 61 mounted thereon to engageand pick up portions of the upper layer 4'?a of ore as they move in thedirection of the arrow 62 in the lower portion of their path of travel.After the upper purified layer of ore has been separated from the lowerlayer 45, the latter layer is broken up by a breaking roll 63 which isprovided with a plurality of longitudinal flutes or teeth 63a adapted todig into the lower layer of ore 45a as the roll is driven in thedirection of the arrow 64. This roll is mounted on a shaft 65 journaledin suitable bearings at the side of the machine and is adapted to bedriven by operating connections extending preferably from the motor 30.The lower layer 45a which vis thus broken up is then in readiness to bedischarged from the sintering pans as these pans move through the gap 3land pass around the curved trackways 19b and 22h. The bucket elevator 58is preferably located ina housing 66 having a discharge'mouth 67 throughwhich the ore picked 'up by the buckets 61 is discharged. Similarly,

the portion of the trackways over which the pans travel during thedischarge of the lower layer 45a is preferably enclosed in a housing 68which is open at its lower end so that the sintered ore may bedischarged therethrough as it falls from the pans 1l. The entire bucketelevator 58 is preferably adjustable vertically so that the buckets61.may be employed for removing upper layers 47a of different thickness.For this purpose, the frame members 69 by which this bucket elevator iscarried are preferably mounted upon adjustable supports.

Although one example of the improved apparatus has been illustrated anddescribed in 1 connection with the explanation of one example of theimproved process of purifying zinc ore, it

will be understood that the process may be practiced in various forms ofapparatus all coming within the scope of the appended claims.

I claim:

1. A process of purifying zinc ores which consists in separatelycrushing and wetting a high grade oie and a low grade ore,thensuperimposing the high grade ore upon the low grade ore in atraveling conveyor, subjecting said ores during their travel to theaction of heat applied directly to said high grade ore at a temperatureand pressure sufficient to free said high grade ore of lead and cadmiumcompounds, condensing the vaporized lead and cadmium compounds in saidlow grade ore, breaking up the upper layer of said ore, and thencontinuously separating said upper layer of ore from said lower layerduring their travel.

2. The process of purifying zinc ores which consists in separatelycrushing and wetting quantities of high grade ore and low grade ore,mixing fuel with said ores, superimposing a layer of said high grade oreupon a layer of said low grade ore, heating said layers of ore by theapplication of heat to said upper layerat a temperature suflicient tovaporize lead and cadmium compounds in said `upper layer whilemaintainconsists in separately crushing and wetting quantities of highgrade ore and low grade ore, mixing fuel with said ores, mixing a smallquantity of sodium chloride with said high grade ore, superimposing alayer of said high grade ore upon a layer of said low grade ore, heatingsaid layers of ore by the application of heat to said upper layersufficient to vaporize the lead and cadmium compounds in said upperlayer while maintaining said lower layer at a lower temperature tocondense the lead and cadmium compounds vaporized from said upper layer,drawing oi the liberated gases from said ores, and then separating theupper layer of high grade ore from said lower layer.

4. The process of freeing zinc ores from lead and cadmium containedtherein which comprises the operations of superimposing a layer of highgrade ore upon a layer of` low grade ore, subjecting the upper layer ofhigh grade ore to a temperature and atmosphere at which lead and cadmiumvaporize while maintaining said lower layer of low grade ore at asubstantially lower temperature kwhereby lead and cadmium arevolatilized from said upper layer and condensed in said lower layer, andthen separating the upper and lower layers.

5. A process of purifying zinc ores which consists in superimposing ahigh grade ore upon a low grade ore, heating said ores by theapplication ofheat to said high grade ore to vaporize the lead andcadmium compounds therein while maintaining said low grade ore at alower temperature to condense therein the vapors from said upper layer,and then separating said high grade ore from said low grade ore.

6. A process of purifying zinc ores which consists in superimposing alayer of high grade ore upon a layer of low grade ore, continuously mov-/ing said layers of ore and applying heat thereto during their travelsuicient to vaporize the lead and cadmium compounds in said high gradeore while maintaining said low grade ore at a lower temperature thansaid high grade ore to condense in said low grade ore the vapors of leadand cadmium liberated from said high grade ore, and then separating saidhigh grade ore from said low grade ore during 'their movement.

7. A process of purifying zinc ores which contheir travel to the actionof heat applied direct- 136 1y to said high grade ore -suflicient toAvaporize the lead and cadmium compounds in said high grade ore,maintaining said low grade ore at a lower temperature than said highgrade ore to condense therein the lead and cadmium vapors liberated fromsaid high grade ore, and continuously removing said high grade ore fromsaid layer of low grade ore during their travel.

8. The process of purifying zinc ore which ccnsists in placing a layerof high grade ore upon a layer of low grade ore in a conveyor,subjecting said ore to the action of heat while moving, in a conveyor tovaporize the lead and cadmium compounds in said upper layer, subjectingsaid heated ore to the action of suction and causing the lead andcadmium vapors to be condensed in said lower layer, continuouslyremoving said upper layer from the moving lower layer of ore, and thenseparately treating the separated layers.

9. The process of purifying zinc ores which consists in separatelycrushing and wetting a high grade ore and a low grade ore, superimposinga layer of said high grade ore upon a layer of said low grade ore in aconveyor, causing said ore to pass beneath a heating means whereby leadand cadmium compounds in said high grade layer are vaporized, thensubjecting the ore to the action of suction means located beneath themoving body of ore to cause the lead and cadmium CERTIFICATE OFCORRECTION.

Patent No. l, 921, 743.

August 8, 1933..

OSCAR GERLACH.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 4,lines 69, 70 and j claim 2,v strike out the words "and condensing thevaporized lead and cadmium compounds in said layer of"; and line 72,after "ores" insert the words and condensing the vaporized lead andcadmium compounds in said layer of ore'. and that the said LettersPatent should be read with these corrections therein that the same mayconform to the record of the case in. the Patent Office.

- Signed and sealed this 14th day'of November, A. D. 1933.

(Seal) F. M. Hopkins Acting Commissioner of Patenti.

